Austenitic chromium nickel steel alloys



Patented May 2, '1939 UNITED STATES 2,157,060 I AUSTENITIC cnaomUMNICKEL STEEL ALLOYS Paul Schafmeister, Essen, Germany, assignor, bymesne assignments, to Krupp Nirosta 00., Inc., New York, N. Y., acorporation of Delaware No Drawing. Original application July 11, 1931,

Serial N0. 550,288.

tion August 31, 1938 Germany July 21, 1930 Divided and this. applica-Serial No. 227,689. In

Experience has shown that austenitic chromium nickel steel alloys thusfar used for corrosion-resisting material cease to be resistant againstattack by chemical agents, lose their metallic ring, become brittle,-and finally even crumble to metal powder when they are exposed to a heattreatment comparable to a drawing treatment of approximately between 500to 900 C., as, for instance, in welding together of individualstructural sections or in use, as for instance, in a process ofhydrogenation. It has already been proposed with considerable successthat for the purpose of making articles of austenitic chromium nickelsteel alloys which either in their manufacture or use are exposed to atemperature comparable to a. drawing treatment, austenitic chromiumnickel steel alloys should be used whose carbon content is below 0 07%or which contain singly or together elements such as titanium orvanadium which form stable chemical combinations with carbon, the

relation between titanium, respectively vane-- I have found that it isnot only the type of chromium nickel steel alloys having a stablesurface, that ls to say, austenitic chromium nickel steel alloys, whicheither have a carbon content so of less than about 0.07% or contain, forexample, titanium, and/or vanadium which have the advantage that they donot lose their resistance to corrosive agents anddo not become'brittlewhen in manufacture or use they are exposed to temperatures comparableto drawing treatments of about 500 to 900 C., but that this advantage isalso inherent in austenitic chromium nickel steel alloys which containzirconium. This elem ment also, as has been p'roveh forms such a stablechemical combination with the carbon in solution in the austenitic basemass that the chemical and mechanical stability of the alloy is notaffected for practical purposes after a heat 5 treatment of about 500 to900 C. In this case,

as in the case of titanium and vanadium, it is also advantageous toestablish such a relation of the stated alloy component with respect tothe carbon that practically the entire amount of car- 60 bon is bound tothe added alloy component. Tests with chromium nickel steel alloyshaving a stable surface and containing 0.12% carbon, 8% nickel, 18%chromium, and 0.3% zirconium show that such alloys still preservetheirresistance to 55 corrosive attack and do not becomebrittle when theyhave experienced heating to about 500 to 900 C.

The zirconium does not burn off to an extent so as to affect thechemical stability of the alloys during or after a heating to about 500to 5 900 C.

The iron content of thealloys forming the subject-matter of theinvention may be as low as 50%, or. even lower.

The chromium content of the alloy may be of 10 the order ofapproximately 12% to 40%, the nickel content of the alloy may be of theorder of approximately 7% to while the carbon content is at least .07%and preferably less than 1%. In the preferred embodiment of theinvention, the alloy contains about 18% chromium, 8% nickel, between 07%and .2% carbon, zirconium about .3% to 2.5%. The zirconium may be usedup to 10%, and should be present in an amount at least suflicient tobind practically all 0 the carbon contained in the alloy.

Austenitic chromium nickel steel alloys, of the type to which thepresent invention relates, are in themselves well known and, asordinarily used, contain about 12 chromium (preferably in 25 theneighborhood of 18%), about 7% to 25% nickel (preferably in theneighborhood of 8%), carbon from .07% to about 2%, and iron,constituting substantially the entire balance (with the exception ofnormal impurities) the iron be- 30 ing substantially all in the gammaform.

One of the principal uses of these alloys is in the production ofchemical apparatus of various 1 types, in which sheets or plates, madeof the alloy, are united by fusion welding. These alloys, however, ifexposed to elevated temperatures of the approximate range of 500 to 800or 900 C., for instance by unitingindividual parts thereof by fusionwelding, and then exposed to corrosive conditions, become liable tointergranular corrosion. 40 If they are exposed, for any appreciablelength of time, to such temperature range, chromium carbides willprecipitate therein, robbing the grain boundaries of 'their protectivechromium, thus permitting intergranular corrosion to occur. Thetemperature range specified may therefore be termed the carbideprecipitation range. The difhculty caused by the formation of thesecarbides, could be cured, as well known, by reheating the metal to atemperature of 1000 C. or

higher, and then rapidly cooling it. Such a process is, however,impracticable, if not impossible, with larger articles, not only becauseit is difflcult. or impossible, to heat them to the necessary hightemperature, and then to cool them to combine with the chromium, thuspreventing intergranular corrosion when the alloy is subjected to thetemperature range (carbide precipitation range) specified, without beingthereafter necessarily further heat treated.

The alloys, containing this addition material, may therefore, ashereinabove stated, be used in the manufacture of metal articles, suchas fusion welded articles, which, in their normal use, are

subjected to active corrosive influences, while the metal in at least apart thereof is in a condition resulting from heating, for instance, byfusion welding, at ranges within the carbide precipitation range,withoutthe necessity of curing, that is, without subsequent heating atsubstantially higher temperatures (and then rapidly cooling); and sucharticles will nevertheless be resistant to corrosive influences, thatis, will not be subject to intergranular corrosion.

Any departure from the proportions specified in my claims which may,however, result in an alloy which exhibits the advantages or myinvention, even though in a less efiective manner, would still .bewithin the spirit of my invention, and of the scope of my claims.

This application is a division of my application Serial No. 550,288,filed July 11, 1931.

I claim: l

1. A metal article which, in its normal use. is subjected to activecorrosive influences while the metal in at least part of the article isin a condition resulting from heating at ranges within the carbideprecipitation range (approximately 500 to'900" C.) without subsequentheating at substantially higher temperatures, said article beingresistant to said corrosive influences and composed of a corrosionresisting austenitic steel, the iron of which is substantially all inthe gamma form, containing about 12% to 30% chromium, about 7% to 25%nickel, carbon at least .07%

but not over 1%, and zirconium in an amount suflicient to combine withsubstantially all or the carbon, but not in excess of 10%, the balancbeing substantially all iron.

2.'A metal article which, in its normal use, is subjected to activecorrosive influences while the metal in at least part of the article isin a condition resulting from heating at ranges within the carbideprecipitation range (approximately 500 to 900 C.) without subsequentheating at substantially higher temperatures, said article beinresistant to said corrosive influences and composed of a corrosionresisting austenitic steel, the iron of which is substantially all inthe gamma form, containing about 12% to 30% chromium, about 7% to 25%nickel, about .07% to .2% carbon, about .3% to 2.5% of zirconiurmthebalance being substantially all iron.

3. A metal article which, in its normal use, is subjected to activecorrosive influences while the metal in at least part of the article isin a condi tion resulting from heating at ranges within the carbideprecipitation range (approximately 500 to 900 C.) without subsequentheating at substantially higher temperatures, said article be nresistant to said corrosive, influences and composed of a corrosionresisting austenitic steel, the iron of which is substantially all inthe gamma form, containing about 18% chromium, 8% nickel, .07 to .2%carbon and about 13% to 2.5% zirconium, the balance being substantiallyall iron.

4. A fusion welded article composed of an austenitic corrosion resistingsteel containing about 12% to 30% chromium, about 7% to 25% nickel,carbon at least .07% but not in excess of 1%, and zirconium in amountsuilicient to combine with substantially all of the carbon but not inexcess of 10%, the balance being substantially all iron.

5. A fusionwelded article composed of an austenitic corrosion resistingsteel containing about 12% to 30% chromium, about 7% to 25% nickel,about .07% to .2% carbon, and about 3% to 2.5% of zirconium, the baiancebeing substantiaiiy all iron.

6. A fusion welded article composed of an austenitic corrosion resistingsteel containing about 18% chromium, about 8% nickel, about 7 to 2%carbon, and about 3% to 2.5% of zirconium, the balance beingsubstantialiy all iron.

PAUL

